The most important things are passport with the valid visa, the ORIGINAL Non criminal record, the ORIGINAL BA degree if you have, the ORIGINAL TEFL/TESOL certificate if you have, the ORIGINAL working reference letters if you have, credit bank card, some two inch photos.
Electronics, such as a laptop, cell phone. Phones can be found relatively cheap in China, especially if all you want is a brick to txt and call. However, if you are planning on bringing your own phone, please remember to unlock it before you come so it isn’t tied to your home network and unusable. You can find out online how to do this. Also, most American phones don’t work with the Chinese SIM network, so Americans should play it safe and just wait until China to buy a phone. You can find a really cheap one for only 200RMB. The plugs in China are three diagonal pronged, with some standard two prong plugs and use 220V, instead of 110 like the US. Other than your laptop, which has a power converter on it, it is advised to not bring other electronics as they might short circuit, especially things like curling irons and hair dryers, which can all be found here, relatively cheap.
There are four seasons in Beijing. You shall pack different seasons clothes and shoes. Clothes are very easy to come by in China. Not only are most sizes and styles available, but also can be found relatively cheap (especially in comparison to western counterparts). One thing to consider however is shoes, mostly for men with US sizes about 12. Large shoes are harder to find in China and you should bring a couple pairs with you.
Since beddings are quite big and heavy, most of the teachers buy them when they are in China, its about 200 Yuan in total for all the beddings.
Bring normal toiletry items such as shampoo, toothbrush, toothpaste, etc. Body care products are often suspected to be in short supply in China; however, there are no shortages of shampoo, toothpaste, conditioner, shaving cream or razors. One thing however, that you should bring with you, is a supply of deodorant, as it is hard to find and there are not many options.
Medicine is not extremely scarce, but it is wise to bring some with you, especially if you know you easily fall prey to certain illness. Ibuprofen is hard to find and I would also suggest some sort of upset stomach relieving medicine along the lines of Pepto Bismol, Immodium.
There is no special dress code, but we need the teachers to wear comfortable shoes and not too tight or sexy clothes. Because the teachers need to interact with the kids, so wearing sneakers and shirt with normal long pants are strongly recommended. 
We recommend bringing around 800USD in cash that you can exchange to RMB at the airport upon your arrival. Or put it in your credit card so you can draw it out at the airport from the ATM in RMB. We do not charge the teachers any money, but keep in mind that you will not be getting paid until after your 1st full month teaching.
You need to pay your health check up, own food, transportation, beddings, SIM card, electricity, water, internet, gas. Health check up is 650 Yuan. Meal is 20-30 Yuan each time. Subway card has 20 Yuan deposit which can be refunded if you leave Beijing and each journey is about 5 Yuan. Beddings are about 200 Yuan in total. SIM card is about 100 Yuan. Electricity, water, internet and gas which are about 200 Yuan/month in total. However the total amount of your monthly expenses is directly related to your spending habits, and also depends on how you budget your money. There is no set level as to how much your living expenses will be because it fluctuates according to your lifestyle. We know some single people who live on about $300 USD a month and others who push it easily over $1000 USD per month. It depends on how thrifty you are and how often you go out. $600 USD is pretty reasonable for a single person. This allows for dinners, drinks, nights out, movies, small weekend trips, etc.